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What would cause an RPM drop and engine cutoff after starting a Cessna 152?
My flight school's Cessna 152 is 30 years old. After refueling, the engine RPM went down and down. I tried putting full throttle in but it just stopped. Was it air in the fuel line or something more serious?

We really don't have enough information to even make a guess here. "Air in the fuel line" seems unlikely however given my (admittedly limited) knowledge of the Cessna 152's gravity-fed fuel system (absent running the tanks dry or the fuel being shut off). Does the flight school's maintenance team have any ideas?

There is only one correct answer.  You must assume that is was something serious and have the mechanics check it out. Only they are qualified to determine the cause.

Happened just once? Perhaps the fuel was contaminated

Two separate events: engine slowing down and engine stalling.  If you are pushing in the throttle too quickly the engine will stall.  Depending on exact year, it is likely that your plane's engine does not have an accelerator pump.  Result: aggressively moving the throttle in will cause a lean condition and the engine will stall.  Dunno about the slowing down part...

I've had this a couple of times... when I forgot to push the mixture forward. :P

Well maintenance said theres nothing wrong with it, fuel was checked and re checked and there was no problem. The RPM after start dropped down and down, till I pushed the throttle full in and out to keep it going. It just stopped. Thanks for the advice thou. I'll be flying in a different 152, that one always has engine problems, especially problems with the starter

Gradual power loss would not be caused by "air in the fuel lines".
The most likely cause is blocked vents. There are pipes that allow air into the tanks so the fuel will flow out. If they are blocked for any reason, fuel will stop flowing, often in a gradual manner.
Another possibility is that there is corrosion or sediment which is blocking the fuel line. Are you checking drain valves on every preflight and after refueling?

It seems a bit odd for blocked vents to cause the problem at ground idle, but  I suppose it's possible (and seems at least plausible). It's actually an easy theory to check if it happens again: Open a tank cap and listen for a "whoosh" of air rushing into the tank to fill the vacuum.


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What vertical flight profile could be expected from an aircraft if the pilots were incapacitated?
If there were nobody at the controls what kind of vertical profile could be expected from, for example, a modern airliner?
After reaching the cruise altitude I assume the pilot just sets a nav route and altitude on the onboard computer or at least set the trim to avoid having to constantly adjusting the altitude manually.

Emergency descent (like during a decompression event where you need to get from cruise to 10k ft ASAP to make sure the people in the back survive) shouldn't make a nice curve. It only wastes time you don't really have.
Normal operation means the pilot activates the autopilot during cruise which will fly the programmed course set by the pilot. It will stay follow that course (or put itself in a holding pattern on the final fix) until it runs out of fuel or the pilot intervenes when it is cleared for descent. This happened with Helios Airways Air flight 522; both pilots were incapacitated shortly after ascent and the plane put itself in a hold and crashed when it ran out of fuel after more than an hour.
A plane where there is nothing controlling the altitude (when control is lost due to loss of hydraulics for example) will follow a phugoid cycle. That is a series of dives and climbs as the elevators gain and lose bite on the air with speed.

Ok i understand that this may fit the profile of an emergency descent. But am i right about thinking that doesnt fit how an unmanned airplane is supposed to lose altitude if no autopilot is set?

@Bolza I added a section for truly unpiloted crafts

A phygoid is unlikely in a naturally stable aircraft with ordinary aerodynamics. It is much more likely to fall into a spiral dive.

@PeterKämpf if the plane is stable in roll then it won't go into a spiral dive,

@ratchetfreak: Yes, indeed. If.

Large commercial aircraft are not expected to descend if their pilots just walk way. At least, not quickly. Large planes generally cruise on autopilot, which will keep altitude until told otherwise. In fact, airliners generally have flight management computers that will fly the entire route before holding near the destination. When the plane runs out of fuel,  it will slow down and then, finally, it will descend until it crashes. This was seen in Helios 522. I don't know what that descent profile would look like.
The Helios 522 accident report shows the following

Aircraft enters from bottom right. AP lines up aircraft with Athens International airport  runway. after overflying airport, AP turns SE and puts aircraft on holding pattern (loop at bottom). Fuel exhaustion causes one engine to flame out and AP to disengage. Aircraft starts to bank (assymetric thrust) and turns. Second engine flames out. Final descent is on a roughly spiral track.

Any descent profile can be expected of an unpiloted aircraft, but generally nothing severe would be expected uncommanded and without stall occuring. Aircraft control surfaces (rudder, elevator, aileron) can be "trimmed" to maintain coordinated level flight.  Elevator trim, in particular, is constantly adjusted (by the pilot or autopilot) so that if nothing was flying the plane it would maintain its present airspeed.  A consequence of this is that a properly trimmed airplane will climb or descent to maintain the airspeed it is trimmed for.
Give the above we can say a properly trimmed aircraft with no pilot input could be expected to roughly maintain altitude and once out of fuel it will descend at whatever rate is required to maintain its trimmed airspeed.
The above assumes no autopilot or an autopilot in speed hold mode.  An autopilot in altitude hold mode will attempt to maintain altitude as long as possible, and depending on the programming that might mean until stall occurs.  When the stick shaker activates preceding the stall, that should disconnect the autopilot and this may be followed by stick pusher activation.  In the end, if stall is avoided, the airplane will descend at the airspeed that autopilot last trimmed it for, which is likely a slow-ish airspeed (close to but above stall speed at present altitude).

All certified airplanes are designed to have a (very slight) spiral instability. The opposite case, dutch roll  instability is not acceptable. This will make a plane that is trimmed out straight and level and then left alone without pilot, autopilot wingleveler or other automation to slowly enter a spiral dive with gradually increasing bank angle and sink rate.
Spiral instability is achieved by having the lateral tail area large enough so when a wing drops slightly by external disturbance and the plane starts to slip in the wing low direction, the tail will turn the plane in the same direction as the wing drop. This is a gentle and harmonic movement, it feels natural to the pilot. If uncorrected it leads to a spiral dive at increased bank angle and speed.
Dutch roll is the result of to small tail area, so when the plane slips for instance to the left, the nose will go right and up. The speed will go down, and if uncorrected will lead to a stall.
It is not the case that a plane left unattended (no pilot or autopilot on duty) will largely stay on course and altitude until the fuel runs out. If a plane was stable by itself, flight in low visibilty would not be a problem.
One famous example is the John F. Kennedy Jr. accident.
http://en.wikipedia.org/wiki/John_F._Kennedy_Jr._plane_crash

This is a very interesting answer! I think it'd be useful to expand on why airplanes must have this instability, and what Dutch roll stability is.

What this answer calls "spiral instability" is a natural consequence of having good yaw stability.  That is, a banked attitude causes the aircraft to turn into the bank, rather than slipping sideways.  Wing dihedral also provides some roll stability, tending to keep the aircraft upright, but if this exceeds the yaw stability a "dutch roll" oscillation can result.  In normal circumstances, heading is maintained either by the pilot or by an autopilot, the simplest being a simple wing-leveller.

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What would happen if a pilot were to use the parking brakes after touchdown in order to slow down?
The situation that I came up with is merely hypothetical. Say a pilot was unable to land right after the runway threshold, for whatever reason it may be - a crosswind, etc - but was determined to land the aircraft.
I understand that most pilots would abort the landing and go around but say this one decides to land. However, it is too close to the end of the runway to stop just by using brakes, spoilers, and the thrust reversers. Could this type of landing (in an emergency) be achieved and by using the parking brakes what would happen if a pilot actually used the parking brakes to slow down?

Not much besides wearing out the parking brake.

On 747-100/200 aircraft there is no separate parking brake. To engage the brakes for purposes of parking, you depress the tops of the rudder pedals as you would for the usual wheel braking, then you pull and hold a lever that engages a hydraulic valve such that the pressure you're holding with the toe brakes is held, then you release the toe pressure you're holding. To release the brakes you, you depress the rudder pedal toes until the pressure you're exerting is greater than the pressure being held by the valve, at which time the vale releases and you're back to normal.

This question appears to have an implicit assumption: that the parking brake would provide more deceleration than is available from normal braking. This is not generally the case.
A much greater worry for pilots than insufficient braking is actually excessive braking - to the point that the wheel locks up and skids. A skidding tire provides much less braking than a rolling one, and also quickly acquires a flat spot. Even on dry pavement, maximum braking would require an anti-skid system to remain effective; consider a 757 and a Mig-29, each of which blew out their tires when their anti-skid systems failed.
Note also that in small planes without complex braking systems, the parking brake merely maintains the pressure that is in the brake lines at the time it's applied. The parking brake would have no effect if the pilot were not already on the brakes, and would not be able to add any additional braking than the pilot could otherwise apply.

Landing with the parking brake set is a recipe to destroy your tires pretty quickly, losing all ability to use your wheel brakes.  I can't remember an aircraft where landing with the parking brake set was NOT prohibited.  Nor can I think of one where the the "parking brake" was anything other than a way to keep the wheel brakes continuously applied -- not a separate brake at all.

I agree with this answer, however as mentioned in Dave's answer, there are some airplanes with abnormal/emergency procedures which actually use the parking brake as a backup system to normal braking, so it is used in some instances.  As you say though, you will need more runway for this than with normal (antiskid) braking.

There is some nice info on this thread and it seems that the parking brakes on large airliners actuate the hydraulic systems as would be expected (unlike in some cars where the parking brake is its own mechanism). It also alludes to the fact that some emergency landing procedures would call for the use of the parking brake.
On a related note, it should be mentioned (and I don't know enough to know if this is actually possible in a large airliner) but I would think you would not want to lock the wheels to the point that they lost traction. This would actually reduce your braking ability.

Antilock brake systems actually were designed for use in aircraft first, and most large airliners and military aircraft have them. However, braking still heats up the tires which are already stressed from touchdown, so excessive braking can blow a tire. Wheel brakes also don't slow you down nearly fast enough in icy or wet conditions. Thrust reversers are typically used where available instead, though noise abatement policies might preclude their use in specific situations

Not quite the scenario you set up, but there was a case where a regional airliner landed with too much speed and too little braking effort. The pilot performed an unapproved and improvised action by applying the parking brake in an attempt to maximize braking. What he did not know was that by applying the parking brake, he deactivated the aircraft's anti-skid protection resulting in reduced braking effectiveness and an overrun down a steep slope.
As a general rule, tires work better at stopping a vehicle when they are rolling than when they are skidding because they generally have greater static friction (gripping) than dynamic friction (skidding). A parking brake is generally meant to keep a stationary vehicle from rolling away, not stopping one. Parking brakes may not be capable of generating enough force to do the job of stopping a vehicle or if they can generate the required force may not provide adequate control to avoid locking up one or more wheels in a skid.
I think the bottom line here is that if it hasn't been written into an aircraft's approved procedures, it's potentially a bad thing.

Everything has greater static friction than dynamic friction; if the dynamic friction were greater than the static friction, the dynamic friction would keep it from moving even if enough force was applied to overcome the static friction - thus making the so-called higher dynamic friction actually, by definition, higher static friction.

Actual RTO (rejected take off) is a certification test that airplane manufacturer must perform succesfully.
In this test the airplane must reach decision speed and abort take-off. When aborting take-off, the pilot should stop the airplane without using the thrust reverses and fire should not be extended to the airplane within 5 minutes (enough for passenguers to evacuate). This test shall be performed using the airplane at MTOW
So, your question addresses a lighter airplane (MLW < MTOW) and thrust reverses can be used. So the answer is yes, it can use the breaks and will work.
I provide you here the video showing the actual test performed by the A340.

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Can test flights carry passengers?
When a new plane is being tested, could it at some phase carry passengers (maybe for free).. Or does it have to be certified, before it can carry a single passenger. Could some one throw some light on any FAA regulation in this regard

Flight tests of new aircraft are covered under Part 21 Subpart B—Type Certificates §21.35 Flight tests.
There is no provision for the carrying of 'passengers' during any test flights, but then, there is no limit on the number of 'flight crew' either. FAA regulations does not explicitly prohibit the carrying of any passengers as such; however, it places onus on the applicant for ensuring the safety of anyone abroad during test flights:

(d) Each applicant must show for each flight test (except in a glider or a manned free balloon) that adequate provision is made for the flight test crew for emergency egress and the use of parachutes.

This places severe restriction on carrying of anyone during test flights. However, before certification, the manufacturer can carry passengers as long as it is not for commercial purposes. Actually, Airbus did this during the test flights of A350 XWB:

Another important aspect of A380 and A350 XWB testing was the Early Long Flights (ELF) programmes, which went above and beyond certification requirements. For these evaluations, a cabin-equipped flight-test aircraft was operated on simulated commercial services with real “passengers” – comprised of Airbus employees – and actual airline flight crews to evaluate cabin systems in typical operating conditions.

Unless the flight testing is at an advanced stage or the manufacturer is extremely confident of the design, I don't see any non-essential flight crew being allowed in test flights, for obvious reasons.
In case of test flights after maintenance or alteration, CFR § 91.407 - Operation after maintenance, preventive maintenance, rebuilding, or alteration says almost the same thing:

(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.

I can't imagine the FAA regulations being much different than the Australian CASA regulations on this one. So you're answer would be No. Only the required flight crew to pilot the aircraft, and a LAME (Licensed Aircraft Maintenance Engineer) if required.

Experimental Certificates and Aircraft Flight Testing are two different things in Australia. Experimental category aircraft are generally home built aircraft that don't get full certification, where flight tested aircraft go through all tests to become fully operational aircraft.


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What are the failure modes for a tachometer in a light single?
During training you tend to get instructed on the various failure modes of instrumentation, such as a blocked static port and its effect on the VSI and altimeter.
This past weekend I had an instrument failure, for which I couldn't really fathom what the cause would be, short of just the dial itself (which may well be the answer!).
Cruising at  3,200ft and roughly 100 Knots the Tachometer just dropped to zero. No engine problems whatsoever, and no incident really, and landed as usual.

Is this likely to be just the failure of the instrument itself, or is there some other failure mode that might cause this whilst the engine runs as normal?

Tachs used in light airplanes have a little DC generator driven by a flex shaft from the engine accessory case. The DC generator is connected to a little volt meter measuring the generator's output, but instead of registering volts, the scale is marked in RPM. The internal drive also connects to an internal multi-stage worm drive reduction gearbox that drives a mechanical drum counter that is geared to display hours to two decimal places. It is geared to run in real time (more or less) when the engine is in its cruise RPM range.
Older car speedometers from the 60s were similar; a speed pointer driven electrically and a mechanical drum rotation counter graduated in miles.
When the dial drops to zero, either the electrical parts inside have died or the flex shaft from the engine has broken.
If the hours counter still counts as you carry on flying, you know it's the internal generator/volt meter has failed. If the counter also stops working, you know its likely that the mechanical drive shaft has sheared.

The counter stopped too, so I guess that indicates the mechanical drive shaft.

I don't know about planes, but AFIR1960s cars were generally strictly mechanical- the speedometer cable went right to the back of the speedo and rotated a magnet inside a metal cup, and also through gears to the odometer.

@Jamiec Probably. The shaft is a sort of small weed eater cable of wire windings in two directions around a core, in a flexible tube. They can fatigue where the wires are crimped into a ferrule at each end. The CRJ200 jet uses flexshafts to drive the flap system (as did the Embraer 145) and that is a failure mode they suffer from from time to time.

Update: You were pretty much spot on. "Morse cable had slipped out the drive" according to maintenance.

I believe your Tacho is of the mechanical type. It is driven by a cable with a static shaft and a rotating core. On one end the cable is attached to the engine's driveshaft, usually through some adapter, and the other end of the cable is attached to the instrument.
The instrument converts the rotation to an RPM indication. This can be done by purely mechanical means (centrifugal force & spring to drive the needle),
or converting the rotation to a voltage and measuring the voltage with an analog voltmeter showing an RPM scale (I guess this is what yours does).
Possible failure points:

the adapter itself doesn't pick up the rotation of the engine (unlikely)
bad mechanical connection of the tacho cable to adapter
a break of the tacho cable core
bad mechanical connection of the tacho cable to the instrument
broken instrument

I suspect the cable is the culprit (2., 3. or 4.) .
I had a similar problem on a 1980's car once, the cause was a cable break near the instrument.
Disclaimer: all I know about tachometers is from fixing a tacho on an old car and fixing an analog speedometer on an old bicycle. I don't have any experience with aircraft tachometers.

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Flying out from an uncontrolled field, should I contact approach or departure at the nearby control field?
I am a new pilot who flies out of an uncontrolled field. When I depart and want to ask the controller for the nearby controlled airfield for flight following, should I contact approach or departure, or it does not matter?

Approach and departure are two facets of the same facility, the TRACON, and it doesn't matter which you call, unless you're an IFR aircraft on an active flight plan or you have a flight plan on file that you want to activate.
For flight following, more important than picking between approach and departure frequencies, is to contact the TRACON on the frequency for the airspace that overlies your position.
For example, at Hollister, the TRACON is called "Norcal," and it handles dozens of different sectors, each with its own frequency.

The frequency for approach and departure at Hollister are identical because that frequency is the arrivals frequency for San Jose International Airport (SJC). That's because Hollister is underneath the approach path for SJC, and that's whose radar screen you will pop up on.

What you should do is look up the frequency for your airport (or for a nearby airport) in the A/FD, in Airnav.com, or in your GPS database, and use that. If it has a discrete departure frequency, then you should probably use that, even though its for IFR departures, but for VFR, it doesn't really matter.

If you want to be pedantic about whether you call the controller "approach" or "departure" think about it this way: If you're going to be flying in (or into) their airspace you're approaching them, so you call them Approach ; If you're in their airspace and departing to go somewhere else you call them Departure. (In practice if you call the right frequency "Call me anything you like, just don't call me late for dinner!")

Hmmmmm, what do you call them if you're en route? Or if you're flying under the departure route of airport A while flying into airport B in the same TRACON?

I've always called them Approach in those situations (because I'm "approaching" the airspace they're concerned with). Approach is probably a good default anyway - in New York it's often the same controller going by two names, and in places where it might not be I think the Approach position is the one that would be more prepared to work with you "long-term" (whereas Departure would expect you to go AWAY)

I believe that Approach is the correct phraseology. First, have a look at these definitions from the Pilot/Controller Glossary (my emphasis):

APPROACH CONTROL SERVICE- Air traffic control service provided by an
  approach control facility for arriving and departing VFR/IFR aircraft
  and, on occasion, en route aircraft.
DEPARTURE CONTROL- A function of an approach control facility
  providing air traffic control service for departing IFR and, under
  certain conditions, VFR aircraft.

The AIM 5-2-7 also says that Departure Control is for departing aircraft only:

Departure Control is an approach control function responsible for
  ensuring separation between departures.

So according to the FAA's definitions, only Approach Control has any responsibility for en route traffic, which includes the scenario you described in your question.
Second, note that the VFR sectional chart always requests en route pilots to contact Approach, not Departure:

FWIW, I was also taught that "Departure" is used only when actually departing a field and that all 'pop-up' communication with the TRACON should use "Approach"; this is in line with the information above.

Seeing that familiar part of the Atlanta sectional was a nice surprise!

I don't think it much matters, and at almost all fields, Approach and Departure are on the same frequency.
But to get really precise about it, I think you should consider it from the perspective of the facility you are contacting.
If you are flying towards that facility, you are essentially approaching it (even if your destination is elsewhere), and should talk to Approach.
If you are flying away from that facility, talk to Departure.


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What factors affect the minimum time to go from point A to point B?

I've created this trajectory for a small RC aircraft to go from 15m to 61m as quickly as possible (e.g. quickest time to get from point A to point B). I'm trying to perform a sanity check for why the aircraft would go to the lowest allowed altitude to maximize velocity before beginning it's climb. Can anyone provide an explanation for why this would be most time-efficient for this problem?
The reason that the aircraft does not fly lower than 5m is because I set 5m as the lowest possible constraint. If that constraint was not in place, it would try to fly at 0m.
Edit:
The reference listed for this type of problem is given as 'J. Betts. SOCS Release 6.5.0, 2007.'. This is an inappropriate place to ask for this, but I have tried searching for whatever this paper/journal this may be referencing and cannot find it. If anyone has any tips/tricks on how to actually find this source, please let me know

You might consider including the formula(s) you used to these numbers. There are quite a few very smart people 'round here who might spot an error, be able to explain why that formula gives the response you're seeing, or suggest a better alternative.

Unfortunately this was created from a software package with a Matlab interface, and they did not provide the mathematical model. I have contacted the publishers, but they have yet to get back from them

Are your points fixed in 3D space, or are you just fixing altitudes no matter where they are reached?

The altitude points were produced as a response to a control input and then interpolated to form a solid line

It looks to me like your airplane, starting with a very low velocity, is trying to climb a height of 46m (61m - 15m).
Because it has a low initial velocity, your basic choices are:

Start climbing immediately, demanding engine power both for velocity and climb rate, and climbing very slowly.
Fly level for a period of time to build up velocity, then begin the climb.
Use gravity and engine power together to get more velocity quickly, then begin climbing at a much faster rate.

The velocity you need to achieve is called $V_y$, or best rate of climb.
Based on the Yellow color on the main segment of the climb, it looks like this plane's $V_y$ is about 26 $m\over s$.
It looks like your software package chose #3.  While it makes intuitive sense, without the math behind it, I cannot tell you the details.

Thank you for the response! The only correction I'll make is that the the velocity being traveled in climb is it's maximum velocity, which is 27m/s. Everything else makes perfect sense to me

@RocketSocks22, 27 m/s is maximum velocity during this manoeuvre, but it is way less than maximum velocity the aircraft is capable of achieving. If you let it fly level, it will accelerate until all engine power goes to compensate drag, but then there is no power left for climbing, so at maximum speed for level flight, no climb is possible. Rather, the speed in climb is the minimum drag speed (that is called $V_y$), so maximum of power is left for climbing (drag times velocity equals power, and weight times vertical velocity also equals power).

@JanHudec, 27 m/s is the maximum velocity for this aircraft based on the motors that I am using. However, you bring up a good point that the aircraft will almost certainly not be able to reach this speed while in climb. I am not certain how I can account for this without seeing the mathematical model being used.

@RocketSocks22, NO, the aircraft can't sustain it's maximum level flight speed in climb. Since the climb from 5 m all the way to almost 24 m is constant speed, it is not its maximum speed for level flight. It is the best climb rate (= minimum drag) speed (the final meter and a bit is a zoom climb that trades some of the speed for a bit more altitude, but the rest only uses engine power).

If you trade altitude for airspeed, then you later have to trade airspeed to get that same altitude back, so how could that ever be more efficient than the other two options?

@StephenSprunk, if the craft is initially flying slower than minimum drag speed, then that tradeoff can make sense.  The energy loss due to drag is cumulative and isn't ever paid back.  The dive allows that drag to be reduced more quickly.

The graph itself presents issues as there is no loss of speed once the plane begins its climb.
Assuming throttle setting is constant, this is impossible.  The plane starts the maneuver at around 15 m/s.  What you need to define is:

stall speed
weight to thrust ratio of your model
best time to climb speed (Vy)

Pulling the plane up at the end to reach altitude would risk stalling and there for would not be very practical in the real world.  Your Vy climb will be the maximum RATE (feet per minute) of climb at full throttle.  Note this is different from Vx, which is the maximum climb per forward distance covered.  Vy is the faster rate of climb.
The climb angle will be a function of weight to thrust (propulsive force) available.
Higher thrust will enable an aircraft to hold Vy at a steeper climb angle.  Based on your data, Vy seems to be around 24.5 m/s.  Notice at the higher angle of climb at the end you start to lose speed. This is drawn correctly. Don't stall!  The part where you begin your climb seems to show a climb at a speed greater than Vy, there for is not the best way.
Notice when you fly a Vy, throttle is at full and you control pitch (climb angle) with the elevator to hold a specific Vy speed (around 70 knots in a Cessna 172).
The dive and zoom is used to reach Vy more quickly and is used in GA aircraft, but is not critical to the analysis.  You might just as easily start from the ground at 0m/s and take off, climbing out at Vy.

That's an example of an optimization problem, the mathematics of which is a significant field in itself. Your case is similar to the renowned "Brachistochrone curve" problem (see Wikipedia).

Yes, I was hoping that someone that someone may have seen a similar optimization problem in their time and could point me towards some resources, as the publishers of the software package I am using have not gotten back to me. Unfortunately it seems that this problem may not be encountered as commonly as I thought it would be. I have not researched the Brachistochrone curve, but I will look into it. Thank you!

This is not an answer to the question.  It does, however, provide some useful information so it would be good as a comment to the original question.

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text:
Experiences with LiFePO4 starter batteries in light aircraft or motorized gliders?
I am interested in real-life experiences to do with using LiFePO4 batteries in light aircraft and motorized gliders compared to standard PbA ones. LiFePO4 seem to be a very attractive alternative to the good ole lead ballast with regard to weight/size and useable capacity.
Points of interest include amongst others:

Operation safety
Handling (e.g. with regard to charging)
Robustness (electric, mechanical)
Compatibility (electric, fittings etc.)
Cost vs. Benefit assessment
Temperature influence
Life expectancy
Technical / legal admission (e.g. insurance-related)
...

This is a very broad question. Even if people do have experience with it, what wold the correct answer be?

@csatlos it is broad and judging the right answer is subjective - would tagging it with something like [tag:reference-request] be useful? In fact all of these aspects are relevant. Any ideas on how to handle questions like these?

It's definitely a broad question, but it's an interesting one. I think it'd be more appropriate with [tag:homebuilt] honestly, because those are the folks most likely to be using these & have the relevant real-world experience to answer your questions. That said, I took a shot from a purely theoretical standpoint below. Take all of it with a grain of salt: My only LiFePO4 experience is as power sources for medical devices, where we like them because they tolerate abusive chargers better than LiCo.

Well, I'll start by saying that (at least to my knowledge, in the USA) there are no certificated/PMA'd/TSO'd LiFePO4 batteries currently available on the market for use in certificated airframes.
That means if you're using a type-certificated aircraft (or an LSA that didn't ship with one originally and for which there is no manufacturer-approved procedure to install one) you're basically out of luck unless you can convince your local FSDO to approve it as a one-off modification to your airframe.
That said, there are some people using them in homebuilts. This guy, for example has used one on his SQ2000 to replace the starter/cranking battery, and there's a company called AeroLithium that sells aviation lithium batteries (albeit uncertified) which some folks seem to be using in (experimental) Carbon Cubs with a good deal of success.

As to the batteries themselves, my aircraft is certificated, I've got no desire to take it experimental, and my relationship with the local FSDO is not one where I could just walk in and say "I want to stick one of these in my plane. Sign off on the 337 form KTHXBYE!" so this is all just theoretical:

Operationally, LiFePO4 is a relatively safe chemistry.
Unlike conventional lead-acid batteries it's not going to spit sulfuric acid on your plane during charging or hard maneuvering.  Unlike other Lithium-based chemistries (say Lithium-Cobalt of Dreamliner fire fame) it's not as prone to blowing up or catching fire if short-circuited or otherwise abused (though puncturing it is still a Bad Thing).
Note however that as LiFePO4 is a lithium based chemistry water may not be the best extinguishing agent for a ruptured/burning battery. One of the potential decomposition products of a burning or ruptured LiFePO4 battery in the presence of water is Hydrogen Fluoride (HF), which is rather nasty stuff.
Handling and Charging is generally normal - as in you can connect it to your aircraft charging system with appropriately-rated breakers/fuses.
Checking cell balance is recommended periodically, but without adequate information on the use of these batteries in aircraft we can't say what "periodically" means -- Every 10 hours? Every 50? Annually? (If installing one of these in a homebuilt I'd start with every 10 hours and work from there).
Robustness should be superior to lead-acid batteries in all respects (mechanical and electrical).
For use in an aircraft a sturdy housing around the cells would be a Must Have to prevent the battery from being ruptured in the event of an incident, but that could be produced reasonably.
Electrically LiFePO4 has a lower self-discharge rate, better tolerance for overcharging, and better (flatter) discharge curves - all Good Things.  It is also stable over a wide range of temperatures, and at least theoretically will outlast lead-acid batteries on a charge/discharge cycle and calendar-year basis (though again, without real-world utilization data we can't really say anything for sure here).
Cost-Benefit is hard to qualify.
LiFePO4 batteries can be had cheaper than "aircraft batteries", largely owing to the fact that they're not approved for use in certificated aircraft.
Because of their higher energy density they're also substantially lighter for the same amp-hour capacity, which is always attractive when we're talking about aircraft applications.
All of those benefits aren't worth a warm bucket of spit to me because I can't install one in my airplane (though I'd certainly consider it seriously if it were a viable option).  If you can install one in your airplane as a replacement for your main battery it may well be worth considering.

Excellent (´cept for the HF part, in one particular plane the battery sits right between my legs)! In Germany, some Ultralights are starting to be sold with LiFePO4 (no wonder, because they do all have a weight problem!).

It actually takes effort to get batteries to pump out HF - they generally have to be punctured/ruptured, and wet. So in the unlikely event it catches fire, use the halon extinguisher - don't urinate on it to put it out! (Of course I'm still not sure I'd want any type of battery right between my legs!)

Well you know how it is - gliders are much prettier on the outside. Cabling and such tend to be quite horrible,  esp. with motorized ones. But your advice re uro-exermination is much appreciated :D


text:
What happens if an engine fails between V1 and V2?
What happens if an engine fails between V1 and V2 on a modern twin airliner?
As I understand it, at V1 you have enough runway remaining to safely stop and abort the takeoff. V2 is the lowest single engine flying speed.
If an engine is going to fail, surely it will be at the worst possible time.

After V1 the pilot will continue the takeoff even with an engine failure. The standard procedure is to take one's hand off the thrust levers at V1 to avoid the temptation of aborting a takeoff if there's a engine failure.

V2 is not the lowest single engine flying speed, in the sense of Vmca.(which has to be lower than Vr and V2 by definition)

If an engine failure occurs above V1 the aircraft can accelerate to the Vr and take-off, retract gear and accelerate to V2 and pass the end of the runway at a height of at least 35 feet. From there, flying at V2 or above the aircraft can climb at angle that keeps it clear of nearby obstacles.
Part of the aircraft's certification is to demonstrate that this is possible.
This question is related to the exact requirements.

To determine the minimum runway length required, two scenarios are calculated. The first scenario has the aircraft accelerating to V1, suffering an engine failure at V1 and then aborting the take-off. This gives the Accelerate - Stop Distance Required (ASDR). The higher V1, the higher the ASDR.
The second scenario has the aircraft accelerating to V1, suffering an engine failure at V1 and then continuing the take-off. This take-off involves accelerating from V1 to Vr, lifting off, retracting gear while accelerating and climbing, reaching V2 and 35 feet at the end of the runway. The runway length required for this scenario is the Take-Off Distance Required (TODR). The higher V1 the lower the TODR. This because when V1 is higher the part of the scenario that involves accelerating on a single engine becomes smaller.
These calculations take into account aircraft weight, engine thrust, aircraft configuration and runway condition.
For the V1 that gives the same ASDR as TODR, the required runway length is shortest. This is called the balanced field length.

This video is an example of an engine failure between V1 and V2. While the aircraft is rotating the engine ingests a heron resulting in big balls of fire. The aircraft lifts of, accelerates and climbs away at angle steep enough to avoid obstacles.
Rejecting a take-off above V1 will likely result in a runway excursion.

V1 is the decision speed, the decision being to continue the take off.  After this, you will take the failed engine into the air.  V2 and VR do not change following an engine failure, nor will you stop accelerating.  Part 25 aircraft must be certified to be able to continue a take off with one engine after V1.

V1 is the critical engine failure recognition speed or
  takeoff decision speed. It is the decision speed nominated by the
  pilot which satisfies all safety rules, and above which the takeoff
  will continue even if an engine fails.

That said, there have been examples of RTOs between V1 and V2.  This FAA paper will give you lots of good data and examples of RTOs both before and after V1.


text:
What is the maximum slope for taxiing aircraft?
Every airport I have encountered has flat runways and taxiways.
Of course this is not exactly true, as some other questions picked up, and it is also possible that I just happened to visit mostly flat airports.
Is there any specification for maximum slope gradient an aircraft can safely taxi on?
A slope could be useful if an airport wanted to build an airplane bridge for example.

I suspect you've visited a limited (and perhaps rather boring) selection of airports.  Offhand, I recall Smiley Creek in Idaho and Alpine County in California as having noticable slopes.  Then there was Nevada Flyers north of Reno, where you generally approached at a 45 degree angle over a gravel pit, touched down on a downslope, then climbed a noticable hill followed by another downslope.

I suspect it wasn't with an A380 right ?

Nope, Piper Cherokee, mostly.  If you want answers that are limited to commercial passenger aircraft (in which I have very little interest), you should say so in the question.

Footnote: I hope this is the correct/ current regulation. Published date is 25 January 2015.
Your question is covered (for EASA regulations) in the document Certification Specifications and Guidance Material for Aerodromes Design (link) in two sections:

Taxiway Slope (CS ADR-DSN.D.265)
Taxiway Slope changes (CS ADR-DSN.D.270)

CS ADR-DSN.D.265 Longitudinal slopes on taxiways
(a) The safety objective of limiting the longitudinal taxiway slope
  is to enable stabilised safe use of taxiway by an aircraft.
(b) The longitudinal slope of a taxiway should not exceed:

1.5% where the code letter is C, D, E, or F; and
3% where the code letter is A or B.

CS ADR-DSN.D.270 Longitudinal slope changes on taxiways
(a) The safety objective of limiting the longitudinal taxiway slope
  changes is to avoid damage of aircraft and to enable safe use of
  taxiway by an aircraft.
(b) Where slope changes on a taxiway cannot be avoided, the transition
  from one slope to another slope should be accomplished by a curved
  surface with a rate of change not exceeding:

1% per 30m (minimum radius of curvature of 3000m) where the code letter is C, D, E,or F; and
1% per 25m (minimum radius of curvature of 2500m) where the code letter is A or B.

(c) Where slope changes in (b)(1) and (2)  are not  achieved and
  slopes on a taxiway cannot  be avoided, the  transition  from  one
  slope  to  another  slope  should  be  accomplished  by  a  curved
  surface  which  should allow the safe operation of all aircraft in all
  weather conditions.

The letters refer to the airport categorization.

Good to see EASA being referenced!


text:
What kind of insulation is used on commercial aircraft?
How are commercial aircraft insulated and what kind of fire barrier material is being used?  How much insulation is required in a typical Boeing 747 vs. a Boeing 787?

most of what is on the aircraft is not flammable, you don't want some faulty wire torching the entire aircraft

@ratchetfreak: You sure don't.

This article from Boeing describes fire safety on their planes, and they mention "fire-protective insulation blankets." A quick google search suggests that in non-aviation contexts, these are usually ceramic fiber. So it seems likely that at least one form of fire insulation in modern transport-class aircraft is ceramic fiber fire blankets.

foil-backed fiberglass is (or at least was) also used, and there are foam insulation products that are popular because unlike ceramic/glass fiber insulation they don't kick up irritating fibers when you cut and work them.


text:
What is the relationship between angle of attack and wake turbulence?
It is said that when the preceding airplane is heavy, clean, and slow, wake turbulence is much hazardous due to greater angle of attack is requried. However, why does increasing angle of attack result in increase in wake turbulence? (or wing tip vortices)

It is not the angle of attack - downwash intensity grows with lift squared and inversely to the squares of wingspan and speed. Please read this answer on how wake turbulence forms. Now let's look at the parameters you listed:

Heavy: Yes, the heavier the aircraft, the more lift needs to be created. Induced drag grows with the square of lift.
Clean: Not really. With or without flaps the amount of lift is the same. Only the lift distribution over span might be different, but this does not make much of a difference for the wake.
Slow: Absolutely! Induced drag is proportional to the inverse of speed squared.

What is missing from the list is wing span which lets induced drag grow with the inverse of its square. The angle of attack is only indirectly responsible for induced drag because lift is (within limits) proportional to the angle of attack.

Wake turbulence is proportional to lift, and lift increases as you increase the angle of attack. Assuming an identical weight and configuration, an airplane on approach will produce less wake turbulence than one in the flare for landing, and an airplane on its takeoff roll will produce less turbulence than one which has rotated.


text:
What is the relation between trim setting and constant airspeed?
I'm having an argument regarding elevator trim. According to a book my friend showed me, trim is for constant airspeed. So, let's say we are flying level at 100 kts with 2300 RPM and it's trimmed. My buddy claims that if we reduce power (1800 rpm for example), and do not touch elevator trim and yoke, pitch will be set for 100 kts by airplane itself and we can descend at 100 kts with 1800 rpm.
However, what I think is to maintain 100 kts with reduced power, the nose of airplane should be lowered and forward trim should be readjusted by a pilot.
Can somebody give me an answer to end this argument?

Your friend is right.  Elevator trim isn't setting a pitch, it is compensating for control forces on the elevator, which vary with speed.  If you are trimmed for level flight at 100 kias and reduce power the plane will initially slow.  As it slows the trim will cause a nose-down moment causing the plane to pitch down.  Given no input, the plane will equilibrate at whatever nose-down pitch is needed to regain the forces it was trimmed for, which means speeding back up to 100 kias.
You are correct that to maintain 100 kias with reduced power the nose should be lowered, but the trim will take care of that for you.
You might have a misconception about how trim works, based on your argument.  A typical trim setup in light airplanes is essentially another control surface on the elevator:

The elevator is the large control surface and that smaller control surface is the elevator trim.  When you adjust the pitch trim you are adjusting this trim tab which provides a force on the elevator that counters aerodynamic forces.  This is why the airplane responds in pitch to maintain constant aerodynamic forces (e.g. constant indicated airspeed) for a given trim setting.

You can test this in the airplane easily.  Take your plane up to the altitude you practice maneuvers at, set 75% power (or some other number) and trim for straight and level.  Add power and watch the plane climb, decrease power and watch it descent, both without touching the trim.  Go back to straight and level and trimmed and accelerate without climbing -- note you are having to retrim as your speed increases.  Decelerate without descending  -- note you are retrimming as your speed decreases.

Good explanation. Two additional notes: 1: because the restoring force affects roll acceleration, the plane will oscillate around the trimmed speed and pitch in a phugoid oscillation, which might be more or less damped depending on particular aircraft type and 2: because the engine thrust is not directly on aerodynamic axis in most planes, the change in power affects the trimmed speed somewhat, how much again depends on particular type.


text:
Do any airlines publish their policy on CRM / Do Not Pair?
A question came up recently on Skeptics.se regarding the implementation of "Do Not Pair" lists in Airline operations. I am skeptical of the answer given (irony?) which ascribes the implementation of the Do Not Pair list to the accident on board Northwest Airlink Flight 5719 - an incident which was in part caused by bad CRM.
However, the NTSB report does not suggest any sort of changes to the pairing of Captain/FO's which is what makes me skeptical that anything such as this actually exists within the industry.
Is there any documented evidence that Captains or FO's can in any way affect who they get paired up with? A single example would suffice.

This story includes lots of references to such a system.

@fooot I'm fairly sure that was the original source of the question on skeptics. I just don't trust layman hack journalists to know what theyre talking about

The LA Times article referenced by Skeptics was written by a flight attendant, and the article I linked also references a book written by a pilot.

@Jamiec yes, it was (or to be pedantic, the exact same article published in Traveller.com.au)

I have certainly heard many airline pilots refer to such a list as a reality at their company, but I cannot offer any hard sources.

To answer your main question only - I would be very surprised if any airline published these types of things. Whether third-parties put them online without the airlines' knowledge is a different story.

Remember this could be a simple has a wife and husband not wanting to risk both of them being prevented from returning home (to look after their children) due to the same aircraft issue.     When I used to write rostering software it was a common requirement to let parners not work at the same time etc.

I worked in the industry for 16 years with multiple airlines.
In two of these we had 'do not pair'. Most airlines use computer systems to do their crew planning. In the systems I have used, you can enter against each crew member, others they should not fly with.
The decision as to the use of this laid with Fleet management or Cabin Crew management and was only used in extremist.
In both airlines however, this was not a documented procedure.
Hope this helps.


text:
What regulatory load cases drive the structural design of aircraft?
What I am looking for here is a sort of a list gathering the manoeuvres and/or load cases imposed by regulation that lead to the sizing of a part of an aircraft. For instance, vertical gust load is often the load case that has to be used to size the structural parameters of the horizontal tail (bending moment). What are the other load cases and manoeuvres that usually size the subparts of a commercial aircraft ?

The applicable US regulation is FAR 25.301-563. This obviously goes into a lot of detail about the different aspects that should be taken into account. I will try to condense the cases as much as possible, but many are conditional and relate to various other conditions. Many cases include some subjectivity as to what the FAA will require. Every certification is unique.
While the requirements are somewhat broken down into the general areas of the plane, it's impossible to say exactly which areas of the plane will be critically affected by a certain case. The impact depends on the design and configuration of the specific plane.
There are the upper level requirements:

(a) The structure must be able to support limit loads without detrimental permanent deformation. At any load up to limit loads, the deformation may not interfere with safe operation.
(b) The structure must be able to support ultimate loads without failure for at least 3 seconds...
(e) The airplane must be designed to withstand any vibration and buffeting that might occur in any likely operating condition up to VD/MD, including stall and probable inadvertent excursions beyond the boundaries of the buffet onset envelope.

Definitions of various important values (which will have structural implications):
VA - Design maneuvering speed
VB - Design speed for max gust intensity
VC - Design cruising speed
VD - Design dive speed
VDD - Design drag device speeds
VF - Desgin flap speeds
VMC - Minimum control speed with critical engine inoperative
VS0 - Stall speed with landing flaps
VS1 - Stall speed, flaps retracted
CN - Normal force coefficient
All strength requirements must be met at all places within the maneuvering envelope, particularly A-I on the following V-n diagram:

Max pitch control deflection at VA (25.331)
Specified pitch control displacement (25.331)
1.5g pullup (25.335)
Discrete gust, vertical and lateral (25.341)

VC: varies linearly

+/- 56.0 ft/sec - sea level
+/- 44.0 ft/sec - 15000 feet
+/- 26.0 ft/sec - 50000 feet

VD: 0.5 times VC values

Continuous gust, vertical and lateral (25.341)
Fuel/oil loads from zero to maximum (25.343)

Addtional factors if there is a "structural reserve" of fuel considered

High lift devices (25.345)

If flaps are to be used for takeoff, approach, or landing, limit load factor of 2.0

+/- 25 ft/sec normal to flight path

Separate conditions, limit load factor of 1.0

Propeller slipstream from max continuous power at VF
Propeller slipstream from takeoff power at >= 1.4 times VF and max weight
Head-on gust of 25 ft/sec

If flaps are to be used en route:

Maneuver to positive limit load factor
Discrete vertical gusts

Maneuver load factor of 1.5 g at max takeoff weight, flaps in landing configuration

Roll maneuvering (25.349)

Airplane load factor 0 and 2/3 of positive maneuvering factor

Steady rolling velocities
Maximum angular acceleration
VA Sudden deflection of aileron to the stop
VC Aileron deflection for same roll rate as VA case
VD Aileron deflection for at least 1/3 of VA case

Unsymmetrical gusts

Yaw maneuvering (25.351), speeds from VMC to VD

Sudden max rudder deflection (conditional definition)
At that max deflection:

Yaw to overswing sideslip angle
Yaw to static equilibrium sideslip angle

Rudder suddenly returned to neutral

Engine torque (25.361)

Limit engine torque at takeoff power and prop speed, 75% limit loads of V-n condition A
Limit engine torque at max continuous power and prop speed, 100% limit loads at V-n condition A
For turboprops, previous conditions with prop control system malfunction
For turbine engines:

Torque from sudden engine stoppage
Torque from max engine acceleration

Engine/APU side loads (25.363)

Limit side load factor

Pressurized compartments (25.365)

All flight loads in addition to pressure differential 0 to max relief valve setting
External pressure distribution in flight
Landing loads combine with max pressure allowed at landing
Pressure including safety factor for high altitude aircraft (>= 45,000 feet)
Sudden release of pressure for critical components

Also affects bulkheads, floors, and partitions

Other emergency depressurizations

Engine failure unsymmetrical loads (25.367)

Failure of critical engine (for turboprops, also failure of drag limiting system)

Speeds from VMC to VD, due to fuel flow interruption
Speeds from VMC to VC, due to mechanical failure

Includes pilot corrective action

Gyroscopic loads (25.371)

Must be considered at max appropriate RPM for certain other cases

Speed control devices (25.373)

Symmetrical and yaw maneuvers and gust conditions, each setting with max speed

If automatic/load limiting features, include corresponding speeds/positions

Control sufrace/system loads (25.391)

Considering other limit load cases

Loads parallel to hinge line
Pilot effort effects
Trim tab effects
Ground gust conditions
Unsymmetrical loads
Auxiliary aero surfaces

Landing load condtions (25.473)

Descent at 10 fps, design landing weight
Descent at 6 fps, design takeoff weight
Both cases should be considered in the following cases:

Level landing
Tail-down landing
One-gear landing
Side loads

Rebound landing
Ground handling
Taxi, takeoff, landing roll
Braked roll
Turning
Tail wheel yaw
Nose wheel yaw/steering
Pivoting
Reversed braking
Towing loads
Unsymmetrical ground loads

Seaplanes (25.521)

Step, bow, stern landings
Unsymmetrical landing
Hull/main float bottom pressures
Auxiliary float loads
Seawing loads

Emergency landing (25.561)

Occupants must have reasonable chance of escaping serious injury in minor crash landing if occupant experiences the following forces:

Upward 3.0g
Forward 9.0g
Sideward 3.0g on airframe, 4.0g on seats
Downward 6.0g
Rearward 1.5g

Large masses should not:

Cause injury to occupants
Penetrate fuel tanks
Block escape

Protection of occupants in dynamic conditions
Ditching strength

Fatigue and damage tolerance (25.571)

Residual strength with certain failed structure:

Limit symmetrical maneuvers
Limit gust conditions
Limit rolling conditions
Limit yaw conditions
Pressure differentials
Limit ground loads

Safe-life evaluation, if failure conditions are not practical
Sonic fatigue
Safe flight with damage from:

4 pound bird at VC at sea level and 0.85VC at 8,000 feet
Uncontained fan blade impact
Uncontained engine failure
Uncontained high-energy rotating machinery failure


text:
Is there an FAA ruling about the airworthiness of piston engines with less than 60 on the compression test?
We've been having some discussions around if there was a specific ruling from the FAA that explicitly said that if a cylinder was showing less than 60 on the compression test, the FAA deemed it unairworthy.  I've heard that, it's a rule-of-thumb and not a ruling, but I don't know for sure.
Has this been conclusively made into a ruling from the FAA, or does it exist as a rule-of-thumb and there are other factors to consider?
This would be specific to United States/FAA and 4-6 cylinder Lycoming or Continental piston engines.

Long story short is that the manufacturers instructions take precedence over all. FAR Part 43 Appendix D requires that at each annual and 100 hr the compression be checked and that if there is "weak" compression further inspection of condition and tolerances of the engine have to be made. Now the term "weak" is kind of broad. FAA Advisory Circular AC43.13-1B states:

If a cylinder has less than a 60/80 reading on the differential test gauges on a hot engine, and procedures in paragraphs 8-14b(5)(i) and (j) fail to raise the compression reading, the cylinder must be removed and inspected.

However, it also states:

This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no manufacturer repair or maintenance instructions.

So the gist of it seems to be that if the compression is below 60/80 on a hot engine IN GENERAL, then yes it needs to be removed and inspected, UNLESS the manufacturers instructions state otherwise. Keep in mind Advisory Circulars are guidelines and not regulatory in nature although they are usually used as best practice guides. There is a great AVweb article The Savvy Aviator #13: Putting Compression In Context that has more in depth analysis.

Mike Busch also did a webinar for EAA called "All About Cylinders" which talks about compression tests (among a whole bunch of other things) - it's worth watching.

Keep in mind that for Part 91 operations manufacturer instructions and service bulletins are guidelines. Compressions are interesting data points but do not give the whole story about cylinder health. A borescope inspection is the best way to determine whether a cylinder needs to be replaced. I currently have one cylinder on my C210 that is below 60/80 and a borescope shows some leakage at the exhaust port, but otherwise the cylinder is fine.


text:
What is the form of information stored in black box?
Black boxes contain the information regarding to a flight. What is the form of those information? Any particular language log?

Related: How much data do FDR and CVR generate on commercial jets?

Also related: Why don't both black boxes hold the same data?

What was missing from the answers you were given the last time you asked this question?

There are 2 different black boxes.

The cockpit voice recorder. This holds audio from several different sources, including the microphone for each pilot, the radio and a general cockpit microphone.
The flight data recorder holds at least 88 different parameters including attitude of the craft, engine performance, autopilot setting, pilot input one the controls, etc.

this answer the question of what data, but the question is rather about how is stored. I wonder why it got accepted, does the OP know what he's asking?

@Federico judging from his other questions I guess not.

Although I have no specific information on this I do work around electronics/computer for a living so if I had to guess...
The older units most likely ran on slow speed audio tapes of some sort, the quality is not great but you can get a lot of time on a single tape. I don't know how the old ones stored flight data or if they even did but tape format would be an option for that as well.
Modern ones most likely store data in solid state chips or on a platter style hard drive. I would think solid state non volatile memory is used (think SD memory card) as its far less susceptible to shock damage than a platter style hard drive. Since these devices most likely use components made for generic purposes the audio could be encoded at any variety of resolutions but is most likely 44.1Khz/16bit or something like that simply because thats what many A/D converters run at.
The flight data may have some custom data format but is stored in some normalized way like any data set on any computer. Maybe JSON, maybe XLM who knows, but things like GPS data have standard string representations that I would think are used. I would think they use some kind of sequential writing on the memory chip so that if something goes wrong mid memory write they can extract based on specific memory locations. Basically if you know that every write of data takes 1000 bytes and you started writing at address 0 you can grab the data from any point in time by directly addressing the memory location.
At least thats how I would design a black box...

I think it is extremely unlikely that JSON, XML or standard GPS (NMEA) is used. These formats are extremely inefficient for storage. Instead a binary format is used.

You are correct that older units mostly used tape, and modern units use SSD's (I don't think they ever used hard drives, as the 1000g requirement would be rather difficult). I agree with DeltaLima that using anything other than a binary data format would be surprising.

My inclination that they used a format like that is more from the fact they would have possibly recycled code from something else but I do agree that they may have their own binary storage format although all formats are technically stored in binary...

@Dave, keep in mind that its simply a big ring buffer where entries are written either periodically or as the data come over the various busses (ARINC 429, the most common data bus in avionics, is one-way, so each sensor has separate wire going from it). The easiest way to implement a ring buffer is with fixed size records. Most likely either exactly as they came or just simply decoded to binary integers or floats.

@Dave, keep in mind that this is a microcontroller. Your typical JSON or XML library wouldn't even fit in it! Also, being safety-critical device, all code on it must be validated and writing validation tests for a JSON or XML library would just be a lot of extra work that is completely unnecessary when all it needs to do is dump the received message at the next address and increment the address counter!

I wrote this some time ago and have learned quite a bit since. Ironically it was around the time I was finishing up a very light HTTP GET/POST JSON library for an Atmel-328 at work, that must have been on my mind....

+1 for looking at the programming side of things on a site started for programmers!

@dalearn I just happen to be a developer/software engineer and private pilot, I know there are a few others on here that are as well.

I think you would be hard pressed to find a Flight Data Recorder that didn't store all of it's data in binary form, packed as densely as possible or in a fixed byte width. I also wouldn't be surprised if it used redundant micros that wrote the same data to two different data storage banks.


text:
What are good resources for learning more about communications?
As title says, which book/web site/etc.. are available for learning proper communication (for Private Pilot License)?

Which jurisdiction?

@vasin1987 why [tag:easa-regulations]?

what is PPL? Play Background Music?

@Him PPL = Private Pilot License around these parts.

@DeltaLima his profile says he from slovenia. I wikipedia it and its member of EU hence easa-regs.

Phraseology?

@DeltaLima thx.

@vasin1987 that makes some sense. However, 99% of the phraseology in the world is agreed upon by ICAO. Individual states may file their local differences from the ICAO standard phraseology in their own AIP. Some European states do. This is outside the powers of EASA.

I do not see why this has been closed. We have other questions asking for resources and those have been well received. What makes this one different?

I've found 4 similar questions that are still open: http://aviation.stackexchange.com/q/9875/3775 http://aviation.stackexchange.com/q/6348/3775 http://aviation.stackexchange.com/q/6372/3775 http://aviation.stackexchange.com/q/9776/3775

This question was put on hold for asking too opinion based question, then I edited it so it's not closed any more.
Previous question was something along the lines recommend me a good resources. And I guess adjective "good" calls for opinion based comments.
Any way, that's that :)

Phraseology is standardized by the ICAO (but countries can notify differences to the standard) in Annex 10 and other documents. The ICAO quick reference guide presents phraseology examples for various situations (taxi, approach, emergency,...). If you are interested in recommendations concerning radio communications in general (not just what directly concerns the pilot), Eurocontrol released a European Action Plan for Air Ground Communications Safety.
Many CAAs also have some form of phraseology reference manual available for free. The general procedures and the phraseology will be almost the same from one country to the next, but variations do occur.

US:

The AIM has a section dedicated to radio communications which details procedures, phraseology and provides general recommendations. Communication examples illustrate the general principles.
The FAA also published an order prescribing ATC procedures and phraseology (but this is a very dry read. Not where I would start)
The Instrument Procedures Handbook contains information regarding radio communication procedures specific to instrument flying (e.g. how to receive a clearance at a non-towered airport)

EU:

Eurocontrol released a guide to phraseology for GA pilots describing good communication practices, phraseology for different flight phases and aviation acronyms. It also has pictures (picture books are always better ;-) ).

UK:

The CAA release a radiotelephony manual describing the phraseology for different flight phases with examples at the end of the manual. It also describes the differences between ICAO and UK radiocommunications procedures (eg FL ONE HUNDRED instead of FL ONE ZERO ZERO).

France:

The SIA has a phraseology training manual with phraseology examples for each flight phase and for using different flight services (ATC, AFIS,...)
The official text for radiotelephony with phraseology in French and English

And many more...

Knowing the phraseology is one thing, but understanding what is being said on the radio can be quite difficult. If you want to practice listening to and understanding radio exchanges, you can find ATC recordings on YouTube or go to LiveATC for ATC communications from all over the world.

VFR Communications for Idiots (West Wings)
Radio Mastery for VFR Pilots Workbook (book)
FAA safety circular on phraseology
The FAA holds regular safety seminars on communication
ICAO Standard Phraseology
Phraseology Guide for GA Pilots in Europe

This is right on the border of being a "link-only answer" - I'm sure you can find a few more things to say besides "Here, click these!"

He asked for books and web sites. I gave him books and web sites.

@TylerDurden What makes these good compared to other resources? Any justification?


text:
What kind of sunglasses are good for flying?
I'm a beginner at aviation. I'm currently in training for gliders license.
Our instructors mentioned that sunglasses are very important if not mandatory.
What kind of properties do I need to look for in sunglasses to determine whether they are good for flying?

None, really. I just don't think they can generate enough lift.

Do not try and find sunglasses. That's impossible. Instead... only try to realise the truth

No polarizing glasses, they make reading anti-glare instruments difficult and sometimes even limit your outside view if the cockpit windows are polarized as well.
Good fit, you don't want to loose them in the slightest of turbulence. Consider fitting a strap so you can temporarily hang them around your neck. They also need to be comfortable if you wear a headset over them.
Neutral colour (grey, grey-green, brown) of the lenses, which does not distort the natural colours too much as that would make distinguishing navigation lights more difficult.

Actually the FAA have published a safety brochure on sunglasses which covers many aspects.

That came as a surprise, as someone who doesn't know much about planes, for some reason I automatically thought that polarizing glasses would be preferred for pilots.

Little known fact: The FAA also requires all pilots to wear sunglasses off duty, at night, and while sleeping.

A photo or 2 would be nice :)

Any advice on finding good quality, non-polarized glasses?  I've looked before, and polarization is a "feature" of most good quality sunglasses.  It seems impossible to find non-polarized.

No matter what type you get in the other answers, make sure they're comfortable.  Realize the headset will be pressing the arms into the side of your head.  I used some Oakleys that I think left permanent dents in my skull.
One thing you may consider as a student is the sunglasses ability to accept a pair of flipdown blinders??(not sure of the name) that are used for IFR training.  Waay better than the hood, but still not as fun as real IFR.

There are some good answers to a similar question here which may help you on some general things. But as mentioned no polarization due to its issues with glass cockpits. Good eye coverage is key and this will depends on your eyes and how different glasses sit on your face. There are lots of low profile sunglasses out there that may look cool but let a lot of light in on top and bottom of the lenses. Also as mentioned they need to fit under your headset nicely so some larger frame stuff wont work that well. I prefer the Ray-Ban aviators (non polarized) with the classic green lens. They sit will under head sets and have nice coverage. Avoid any lens that has a gradient tint, I tried to fly with a pair of gradient tinted aviators I also own and it was miserable.


text:
Could the stick position be used as a Angle of Attack indicator?
True or False: The stick determines elevator position and elevator position determines angle of attack. When the critical angle of attack is exceeded, the wing stalls. So, given a design with enough elevator authority, if the stick is in your lap, then the wing is stalled. If the stick is, say an inch farther forward, the wing will not be stalled. Let's stipulate no flaps/slats, calm air, normal CG, positive G, and plenty of elevator authority. Maybe use a plane such as the Luscombe 8A for the sake of this discussion. That will keep things straightforward.
I guess the crux of what I'm asking is: why couldn't the stick be used as an angle of attack indicator? Let's assume a pilot is able to very precisely detect the stick position, or that maybe an indicator is installed in the panel which is connected to the bottom of the stick under the cabin floor.

You can (and probably have in training) fly to the edge of a stall with the stick at a certain position, then apply some power to keep flying, with the stick (or control wheel) at pretty much the same position.  (I say "pretty much" because you don't really pay that much attention to the exact position, you just fly the plane :-))

There is another parameter involved: Pitch rate. A higher pitch rate will need a more backward stick position for maintaining AoA.

The direction of the inflow to the wing plays an important role, too. In the course of a mushing descent, or in a sideslip, for example, the attitude and horizontal airspeed of the plane may remain more or less constant, but the sink speed tends to rise. Hence, the AoA increases, and may easily reach the critical, stall value.

@PeterKämpf What do you mean by "pitch rate"?

Rotation around the lateral axis.

Okay. I think quiet flyer below was talking about this. He called it "pitch damping."

Stick transducers exist already and are not difficult to mount, in fact they provide inputs to Flight Data Recorders already. It is one of the inputs to AoA. There is no substitute for direct measurement of the variable.

You may read how it flies

For a given set of configuration parameters, CG, weight, power, G loading, you could theoretically use stick position as an approaching stall indication.  Problem is, the actual location would vary with all those parameters, so if you had a stall indicator device that was measuring and displaying stick position, you would constantly have to vary the calibration with power setting, flap position, G load, all up weight, and center of gravity.
So, take the apparatus you would have developed to go under the floor to measure where the stick is at, and move it out to the wing with a vane that gets blown on in the clean air flow, have THAT drive your indicator, and voila!  No need to adjust for any configuration variables and you know exactly where you stand relative to stall at all times and in all flight regimes.

So you must be saying that a given stick/elevator position doesn't necessarily set the wing to a specific angle of attack. You mention "CG, weight, power, G loading." Are there others? How does each affect what angle of attack is achieved for a given stick/elevator position?

I like your answer better...

There are many other inputs into the AoA. Stabiliser deflection. Landing gear extension. Flap deflection. Vertical speed.

@birdus as Koyovis and Peter mention there r just so many variables that change elevator deflection required to get a given airplane AOA/speed.You COULD predict AOA for a given stick position,for a fixed set of physical parameters,in level,un-accelerated,1G flight,in smooth air,but the instant any of those things changes your prediction would have to change. Almost all light aircraft use indicated airspeed,which gives a reliable indication of AOA margin for a given physical config,but only in stabilized un-accelerated flight at constant power.U have to measure AOA directly cover all the bases.

I'm going to contradict everyone just a bit and say that the idea has some merit.
If we consider the problem mathematically, in perfect conditions (calm air, straight and level flight, const everything), then it may be useful to think of elevator control as an AoA control. Many people, including pilots, fail to realise the strong link here. So at least for educational purposes we can say yes.
However, even in such conditions we must stress that we are only talking about steady state conditions, when everything settles on steady/const values again. When you move the stick (which you can do very quickly), the aircraft doesn't react instantly (nor strictly proportionally). There will be transition effects of varying complexity, and much of the Flight Dynamics science studies just that. Nevertheless, a 'good' stable airplane will settle on something (as long as it has capacity for that, e.g. power), and this new AoA will reflect the new stick position.
For this reason, in practice it is more useful to think of the elevator trim controlling the steady AoA than the elevator itself: we normally use trim for exactly such steady conditions, and use elevator for 'dynamics'.
Of course, as everyone said, in practice there are many more variables (which actually vary), and a proper AoA sensor is not so complicated. Even the stick/trim position for a given steady state AoA will vary depending on the CG location, as it will need a different amount of travel for the same effect. Nevertheless, there are some practical cases when the stick position makes a reasonable proxy for AoA, even despite having an AoA sensor.
First, the stick allows to separate intentional AoA changes from accidental ones (e.g. due to gusts). Sometimes it matters. Second, it may be faster (for intentional changes): the stick will show the desired AoA before one is actually reached. These two things are used in at least one control system I know: the nose cone control of MiG-21bis.
The cone needs to be moved forward at higher AoAs, so that the supersonic shockwave didn't get inside the intake. Yet you don't want to move it constantly with every little gust; at the same time, the drive is not that fast and you want to pre-empt it before the dangerous AoA is reached. So the stick position is used as an input for this system on this aircraft, instead of the true AoA (which is available).

Stick position is indeed a rapid input, AoA and cone deflection are responses to the input. Good point.

Phrasing this a bit more pithy:  If you are flying straight and level, and pull the stick back beyond the "stall line," the plane will not stall immediately.  Likewise, if you are in a stall, and let go of the stick, the plane does not immediately recover.

Good answer which could be improved by mentioning the cg position: A more forward cg requires more stick travel for trim, so the stick positions will differ at the same AoA and different cg.

Good point @Peter, added.

The aircraft's dynamics certainly relate angle of attack and stick position, but they are not one-to-one related. There are complex dynamics involved. Some examples:

You can take the stick and at a slow aircraft speed rapidly cycle it back and forth to the stops, and the aircraft's AOA will not track with it. The response of the AOA to the stick position is not instant (at slow speeds).
You can fix the stick and fly into turbulence, and the AOA will be all over the place while the stick is fixed. Again, its a dynamic model relationship between stick position and AOA.
You can shift the CG position by burning off fuel, and the stick position/AOA relationship will change.

Langewiesche's "Stick and Rudder" emphasizes the idea that the elevator is fundamentally an angle-of-attack control, and that limiting the aft motion of the control stick will prevent the wing from reaching the stall angle-of-attack.
But here is a fundamental problem with the idea of using the control stick as an angle-of-attack indicator-- it may work fine in wings-level, non-accelerated (non-looping) flight, but in turning flight, the stick must often be positioned MUCH FURTHER AFT to set the wing at a given angle-of-attack than in wings-level flight.
For example when a sailplane is thermalling, the stick is often quite far aft-- at a position that would produce a stall in wings-level flight.  This is especially true if the CG is rather far forward.
There are several sailplanes (example: Slingsby Swallow) that have been designed to have rather limited elevator throw in the interest of stall prevention, in which heavy pilots flying near the forward edge of the allowable CG envelope find that in a thermal turn, even placing the stick full aft against the aft stop produces an angle-of-attack that is clearly lower than the angle-of-attack that would yield the minimum sink rate.  In other words, they are forced to fly too fast.  Even though those same pilots could slow down well below the minimum sink-rate speed, and perhaps even all the way to stall speed, in wings-level flight.
Several faulty explanations have been offered as to why this is so.  The truth is, if the flight path is curving, then the relative wind is also curving.  Or to put it another way, since the aircraft is rotating in both pitch and yaw, as well as translating linearly, the rotational motion induces a difference in the direction of the local relative wind between the nose of the aircraft and the tail of the aircraft.
Loosely speaking, in a moderate to steep-banked turn, in the aircraft's reference frame the nose is constantly "rising" and the tail is constantly "falling", and so the curving relative wind tends to "push up" on the tail and create a nose-down pitch torque, placing the wing at a lower angle-of-attack than we'd see with the same stick position in wings-level flight.
This can also be described as a "pitch damping" effect-- the aircraft has an inherent aerodynamic resistance to pitch rotation, and this aerodynamic resistance is expressed as a nose-down pitch torque that causes the wing to fly at a lower angle-of-attack than we'd see for the same elevator position in wings-level linear flight.
These effects are much more pronounced in slow-flying aircraft than in faster-flying aircraft with the same linear dimensions, because the radius of curvature of a turn is inversely proportional to the square of the airspeed.
If this all seems a bit implausible to you, you might want to read the article "Circling the Holighaus way", which deals with the effects of the curving relative wind in the yaw (not pitch) dimension.
http://www.wisoar.org/Documents/Holighaus%20-%20Thermalling%20Efficiency.pdf
Also note that in a pitch "phugoid", either with the elevator allowed to float freely or with the elevator firmly held in a completely fixed position, it can happen that the stall horn sounds as the flight path is arcing downward near the top of each oscillation, but is silent as the flight is arcing upward near the bottom of each oscillation.  Again this is a manifestation of the way that the curvature in the flight path and relative wind causes an increase or decrease in the wing's angle-of-attack.

Also as another answer implied, there are issues of inertia and lag.  There's no doubt that you can place an aircraft in a very nose-high climbing trajectory where it will eventually run out of energy and whipstall, even with the stick not too far aft.   Again though this may be viewed as a function of the radius of curvature of the flight path.

As an aside, I once did some experiments involving a device that could be clamped on to the tube that comes out of the instrument panel of a Cessna 152/72, to which the yoke is attached.  This device created an artificial stop limiting how far forward the control yoke could be pushed.  When the yoke was held firm forward against this stop, the elevator position was fixed in the fore-and-aft sense yet the ailerons could still be used.  I carried out experiments involving rather rapid transitions from 45 or 60 degree banked flight to wings-level.  The results were a bit interesting (alarming)!

The device was basically the type of vice grip that is used to hold sheet metal, with rubber padding glued on.  Like this.  https://www.amazon.com/IRWIN-VISE-GRIP-Original-Locking-23/dp/B0000TFGFU  The most interesting/ alarming results involved pitch "phugoid" dynamics in which changes in angle-of-attack did not necessarily play a key role.  However, if one set up the plane so that the stall horn was barely sounding in wings-level flight, the stall horn would go silent once the plane was established in a banked turn, with the elevator in the exact same position.

Also note that for a given fixed position of the control stick or yoke, and assuming no cable stretch, the position of the elevator trim tab will have some small effect on angle-of-attack, acting in a "reverse" sense-- nose-up trim will cause the wing to fly at a slightly lower angle of attack than nose-up trim, for any given position of the elevator.  This only pertains to cases where pitch trim is accomplished by a trim tab on the elevator and not some other means.

False.
The problem is, even with all your stipulations, there are still things that can affect the AoA besides stick input. For instance, you stipulated "normal CG" without defining what, exactly, that means. Most pilots on hearing that phrase would assume you meant "somewhere between the fore and aft limits" -- i.e., where the CG "normally" is. But the CG can vary within that range, changing the airplane's pitching moment, thereby changing the relationship between the stick position and the AoA.
But what if we stipulated that the CG was at a fixed, known location? There's still the issue of airspeed. The more air flowing across the elevator, the more control authority you have, so the same input creates a bigger AoA change.
But what if we stipulated that the airspeed was fixed? Then there are probably several other factors that I can't think of right off the top of my head that also affect the AoA.
But what if we stipulated that all these other factors are fixed as well? Then you still have the issue that the AoA would lag behind the stick position due to the inertia of the airplane. That changes your theoretical AoA indicator into more of a what-the-AoA-would-be-if-you-haven't-moved-the-stick-recently indicator.
But, if you add all these other stipulations, and find some way to compensate for the lag, then the answer to your question becomes true: you can use stick position to calculate AoA.

Let's try a concrete example. Suppose I'm flying along, straight and level, at a 3° Angle of Attack. I want to climb, so I pull the stick back. What happens to the AoA? All I've done is rotate the plane, I haven't actually changed the direction of flight (yet), therefore the AoA starts increasing. Increasing the AoA increases lift (as long as you haven't stalled, that is), so now the lift is greater than the weight, so the airplane starts to climb. This, in turn, changes the angle of the relative wind up until it reaches an equilibrium based on the speed of rotation of the airplane.
The AoA is maintained at this equilibrium point by aerodynamic forces. If the AoA decreases below this point, then the airplane loses lift, so the relative wind can't keep up with the rotation of the plane, which increases AoA. If the AoA goes above this point, then the airplane gains extra lift, so the relative wind starts to catch up with the rotation of the plane, which reduces AoA.
But anything that rotates the plane will have the exact same effect. Let's say a big guy gets up from the front seat and walks to the back. This produces a rotating moment that tries to pitch the plane up. If nothing is done to balance this, then the plane will start to rotate, producing the exact same effect of changing the AoA, causing a climb, which changes the relative wind until it finds its new equilibrium point.

For the sake of this discussion, I guess I assumed people wouldn't be imagining that the CG was moving around, but was at only a single, specific location.

@birdus The CG does change during flight. If nothing else, the fuel draining from the tanks will cause the CG to slowly wander away from where it was. But I was referring more to the change in CG from one flight to the next. If you're trying to create a general-purpose AoA indicator, it would have to work regardless of if you have passengers in the front, passengers in the back, cargo, etc., etc., etc.

I'm trying to understand physics, not design an angle-of-attack indicator. For the sake of argument, then, use a glider or an electric airplane. And why would CG have to change for a gas powered plane? If the tank(s) is over the CG, then CG might not change at all.

For a gas-powered airplane, the odds that the gas tank would be directly over the CG for any given flight is vanishingly small. But if that did happen, then, yes, the CG wouldn't change as the gas drained. As far as understanding the physics: I think maybe a concrete example would help, but that's a little long for a comment, so I'm going to edit my answer instead.

Relative stick position is a good "seat of the pants" gauge for knowing when you are close to a stall, but stick feel will change with trim and therefore isn't reliable indicator of stick position.  So yes, there is a correlation between the two that can be useful, but position alone should not be used as a primary means of determining critical AOA.  Also, Angle of Attack has a precise definition associated with it.  While stick position influences AOA, it doesn't meet that definition so the two should not be confused.

But trim just moves the elevator (and thus stick) preemptively. How does that change anything? I believe all trim would do is change the force you'd need to apply to the stick to get it to whatever position. Let's be precise. You said trim changes "feel." Can we agree that we're not talking about feel here? Second, you said position can change with trim. Do you mean that trim will change the angle of attack for a given elevator position since the elevator has a very slightly different shape for varying degrees of trim?

OK, I edited my answer a little to be more precise.  I guess I don't have a complete understanding of what you are suggesting.  Do you think a stick or yoke position indicator would be useful for a pilot to know when he/she is approaching an impending stall?  Because I don't agree with that.  I think there are more and better options.

When trim is implemented with trim tabs, and the elevator controlled by simple pulley, the same elevator coefficient of lift (and thus trimmed AoA) will correspond to the same stick position. However it is no longer the case when trim is implemented with a movable stabilzer (as airliners do), the coefficient of lift will change more when the whole stabilizer moves. And then the pilot can judge the force on the stick quite well, but judging the position is much harder as there is not much of a reference for it.

The trouble of using the stick position as stall indicator is that even with the stick at neutral, I mean not touching it, you may get stall just by acting on the trim. Several solutions to prevent stall do exist; in addition to the stall warning the Boeing philosophy on B777 is to modify the stick load. Airbus too has a solution by which the stick instead of giving a proportionate deflection to the elevator, it gives a load factor order that becomes limited when you get close to the critical AOA, the critical AOA being function of the configuration that is flaps, slats etc, by this technique pulling fully the stick does not cause stall; Airbus uses 3 AOA sensors to isolate a faulty sensor.

FALSE
This actually is a very dangerous assumption.  Firstly, there is a relationship between CG and elevator pitch that can be learned from paper airplanes and simple balsa gliders. Learning the basics of unpowered flight is essential to understanding AOA and stalling, as well as appreciating the importance of being within CG limits.
AOA is dependent on the relationship between Clift, CG, and pitch (stick position AND trim), and airspeed.  A plane set up with forward CG and up elevator by design will raise its AOA at too high a speed and lower it as speed bleeds off from climbing and increased drag.
Notice as the plane climbs the relative wind also changes on the tail, raising the nose even higher, but the forward CG and lowering airspeed lessen the pitch up effect.  Eventually, the plane stops climbing and the relative wind again changes on the tail, pushing the nose down as it sinks.
Now move the weight back for the same elevator setting past the aft CG limit.
As the plane climbs and slows, the nose keeps rising.  AOA will increase to the point of stall.
In models this produces a smooth level flight as the aircraft obeys the laws of physics:  higher AOA increasing lift cancels lower speed decreasing lift, up to the point of stall, where it will abruptly pitch down.
So really airspeed is what you need to keep an eye on.  At a CONSTANT airspeed, a given pitch setting will give a given AOA assuming no change in relative wind (see Quiet Flyers work describing thermals).
Too many factors in real flying to make stick position useful beyond a general approximation.

My 5c worth

Power is what causes climb or decent .
Stick will change position with application of trim or pilot input .
As a rough guide I do think stick position is a general proxy for AOA
The discussions regarding turns don’t contradict this as in any turn if you want to maintain altitude you need to pull back on the stick i.e increase AOA and apply power .

In summary trim moves the stick so just unloads the pilot input pressure required on the control . Next step will be to rig up a sensor and do tests over different flight flight conditions . I purchased a LRI indicator at Oshkosh 2007 and it was basically a pressure sensor with a pickup outboard on the wing measuring air pressure at different points on an angles aliminum section , much like the dynon AOA pitot tube. There are always various views on these devices but experimenting and thorough flight testing ( if safe ) should always be encouraged as that helps us move forward.

uh, no. Trim does not move the stick. In fact the trim tabs are there to reduce the need for constant stick input. Trim+stick position+thrust determine AOA together (in combination with the design of the airfoil).

hmmm... try it. Let go of the stick (first trim to level flight of course), then change trim and see if the stick moves...